1. Field of the Invention
The present invention relates to high performance, crosslinked thermoplastic hoses capable of withstanding high temperature and having chemical resistant characteristics, and more particularly, to a method for preparing such crosslinked thermoplastic hoses.
2. Description of the Prior Art
Hoses, particularly curved hoses such as those used to transport fluids in automobiles, typically, are manufactured by positioning a pre-cut length of uncured hose over a curved mandrel and then heating the mandrel and curing the hose so that the hose retains its desired shape. The hose may be solely an elastomeric hose or it may be surrounded or have incorporated therein a twined reinforcement. Optionally, a cover of the same or different material may surround the hose. Typically, the hose is prepared from a heat curable elastomer by placing the extruded hose over the mandrel which is heated to cure the hose. The cured hose is then removed from the mandrel while the mandrel is hot to facilitate easy removal of the cured hose from the mandrel. One such method is described in U.S. Pat. No. 4,537,736 to Peltzman et al. Such hoses have been used in a wide variety of applications such as fuel feed hoses, torque converter hoses, air conditioner hoses, power steering hoses, etc. However, in general, such hoses do not have sufficient abrasion resistance necessary for some specialty hoses, nor do they exhibit high tear strength; and prior art attempts have failed to improve these characteristics beyond certain limits. For example, U.S. Pat. No. 5,476,121 to Yoshikawa et al discloses rubber hoses having improved barrier and flexibility performance by providing an inner hose of a synthetic resin having an outer peripheral surface, forming a thin film of silver or a silver base alloy on the outer surface of the inner hose, and heat curing the rubber layer.
High performance hoses such as power steering hoses require high resistance to both chemical and temperature degradation. At present, power steering hoses and other high performance hoses are made from compounded elastomers such as a chlorinated polyethylene, a chlorosulfonated polyethylene or similar materials capable of withstanding temperatures up to 300.degree. F. and the chemical effects of power steering fluids. Chlorine-containing polyolefins including chlorinated polyethylene and chlorosulfonated polyethylene generally possess good mechanical properties, good compression set, good low temperature flexibility and good dynamic fatigue resistance. These materials also exhibit excellent aging, weathering, chemical and ozone resistance due to their saturated backbones. However, in order to withstand high temperatures of about 300.degree. F. and chemical resistance to power steering fluids, hoses constructed of such materials must be built and vulcanized on a mandrel and then removed from the mandrel for additional processing. The manufacture of elastomeric power steering hose on a mandrel is described in U.S. Pat. No. 3,972,757 to Derderian et al. U.S. Pat. No. 5,683,773 to Kemper, and U.S. Pat. No. 4,110,396 to Reynolds teaches an automotive hose where the inner hose or, preferably, the cover portion is formed of an elastomer comprising a chlorinated polyethylene-based elastomer or polyether-based elastomer stabilized with barium sulfate.
In view of the cost associated with manufacturing high performance hoses such as power steering hoses, it is desirable to provide materials having the desired characteristics but which are easily formable without the use of a mandrel while providing improved performance and reduced overall costs.